FIG. 1 is a schematic diagram outlining the treatment of phosphate ore after it is mined. The phosphate ore retrieved from the ground is in the form of “matrix” which includes phosphate pebbles sand and clay. After mining, the matrix is pumped in pumping station 3 from a dragline 1. The matrix is pumped into washing equipment 5, which produces pebble product, waste clay and small particles. The small particles are sent to sizing equipment 7, and then subsequently to flotation equipment 9.
FIG. 2 is a schematic diagram of the washing equipment shown in FIG. 1. From the pumping section 3, the matrix is supplied to a receiving section 501, which receives and decreases the velocity of the incoming matrix. The matrix is then sent to scalping screens 503 (“trommel screens”). The function of the scalping screens 503 is to scalp out particles that are greater than 1 inch in diameter (+1 inch). The particles that are smaller than 1 inch in diameter (−1 inch) go into a matrix tank 505. The +1 inch material goes into a mudball slicer 507. The mudballs enter the mudball slicer 507 in a relatively dry state and are sliced using high-pressure water. The water breaks up the mudballs, without necessarily creating a slurry. After breaking up the mudballs, the material is sent through another screen (not shown) to perform the +1 inch, −1 inch separation shown. The +1 inch particles form a waste stream. The −1 inch particles are sent to the matrix tank 505.
In the matrix tank 505 water is added. A portion of the fine clay floats during this operation. The floating clay from the matrix tank is sent to de-sliming. The remaining particles are sent to log washers 509. In the log washers, shafts with paddles thereon rotate in a tank causing the incoming material to be ground such that smaller clay particles are broken down. The incoming feed to the log washers is a slurry, perhaps containing 30% solids. These solids are particles having a diameter of less than 1 inch, and include phosphate particles, sand particles and clay particles. The log washers perform grinding and scrubbing on the incoming materials due to inter-particle friction caused by the movement of the paddles attached to the rotating shaft.
From the log washers 509, the material is sent to screens 511, which separate out a phosphate pebble product having a diameter larger than 1 mm. This phosphate pebble product is a phosphate concentrate that can be subsequently used without further processing. The particles smaller than 1 mm do not have a sufficiently high phosphate content for further processing. The particles less than 1 mm in diameter include sand and phosphate particles, which are about the same size and weight, thus making difficult other separation techniques.
These smaller particles are coated with clay and are sent to a de-sliming to remove clay. FIG. 3 is a schematic view of the desliming process. In FIG. 3, hydrocyclones are used to separate finer and coarser particles. The finer particles exit over the top of the cyclone and contain clay. The finer particles are sent to waste clays. The coarser particles are considered clean feed. The coarser particles exit from the bottom of the cyclones and are sent to sizing.
FIG. 4 is a schematic view of a sizing process. In FIG. 4, the particles are sent to a series of sizers. The sizers include a fine sizer 701, a coarse sizer 703 and an ultra coarse sizer 705. From the various sizers, the particles are sent to separate storage tanks before being supplied to flotation 9. The flotation process must run continuously, and one purpose of the three-storage tanks is to provide a buffer to compensate for any flow problems occurring before or during sizing. The fine, coarse and ultra coarse particles are collectively referred to as “feed” material.
FIG. 5 is a schematic view of the flotation process 9 shown in FIG. 1. After the feed is de-slimed and sized, the fine, coarse and ultra coarse particles are separately floated. After sizing, the particles are stored in water. The first step in flotation is to remove this water in a dewatering cyclone 901. Water is removed such that the feed is perhaps 70% solids. In the dewatering cyclone 901, fine clay particles exit as an overflow stream (not shown). Throughout the treatment process described above, clay removal is important because steps subsequent to dewatering employ chemicals, and the clay acts as a diluent for these chemicals. With less clay, smaller amounts of chemicals are required, thereby reducing operating costs. From the dewatering cyclone 901, the particles are sent to a conditioning process 903. During conditioning, reagents are added to the feed, which is substantially free from clay after the dewatering cyclone. The pH is increased, perhaps to about 9. For example, a 70% solution of soda ash may be used to increase the pH. Also during conditioning, a fatty acid/tall oil reagent is added. Due to the surface chemistry, the reagent coats the phosphate particles. The reagent does not coat the sand particles. After conditioning 903, the coated particles are sent to a rougher flotation process 905.
The coated phosphate particles are hydrophobic. In the rougher process 905, air is bubbled through a flotation column or other flotation machine. The coated phosphate particles float to the top of the column or other flotation machine because of the incoming air. The phosphate particles, which float off the top of the column, are collected and sent to acid scrubbing 907. The sand particles are not coated and do not float. The sand particles exit from the bottom of the rougher process 905.
The hydrophobic phosphate particles, along with some fine sand particles, are sent to an acid scrubbing 907, where an acid, such as sulfuric acid, removes the fatty acid/tall oil mixture coating the phosphate particles. After scrubbing, the particles are sent to a cleaner flotation process 911 where an amine solution is used. The amine solution causes the sand to float off the top of the column leaving behind the substantially clean phosphate concentrate product.
Although the foregoing process works well, there are many steps, and it is expensive to run. Various attempts have been made to improve the process. For example, Jacobs Engineering Group, “New Technology for Clay Removal,” Publication No. 02-138-177 (Florida Institute of Phosphate Research, 2001) proposed to use a vibrating ramp to separate mudballs. An ultrasonic generator caused vibrations in the ramp. However, there was no direct contact between the ultrasonic waves and the material. It was not possible to deliver enough energy to separate.